There are various known semiconductor devices, such as semiconductor memories. Among these memory devices, those that hold data even when the power source is turned off are called nonvolatile memories. Among the nonvolatile memories, one using a ferroelectric material as a capacitor material for holding the electric charge is called ferroelectric memory (Ferroelectric Random Access Memory (FRAM, registered trademark)).
The FRAM utilizes two residual polarizing properties of dissimilar polarities possessed by a ferroelectric thin film, and holds data even when the power source is turned off. The possible number of times of rewriting, which is an indication of nonvolatile property, is as great as 1×1010 to 1×1012 times. The rewriting speed is in the order of several tens of nanoseconds, a very high speed.
In the FRAM, the ferroelectric material used for forming a capacitor can be polarized in one of the two directions. By distinguishing the direction of polarization, it is possible to store the data “1” corresponding to one direction of polarization and the data “0” corresponding to the opposite direction of polarization. When the dielectric material in the capacitor is not a ferroelectric material but is a paradielectric material, the polarization is maintained only when there is a potential difference from the electrodes but is not maintained when the potential difference is removed. In this case, therefore, a volatile operation is brought about. The direction of polarization of the ferroelectric material in the FRAM can be detected by applying a potential large enough for switching over the polarization of the capacitor.
The ferroelectric materials used in the FRAM include a lead-based ferroelectric material and a bismuth-based ferroelectric material. Representative lead-based ferroelectric materials are PZT (PbZrxTi1-xO3), PLZT (PbyLa1-yZrxTi1-xO3), etc. A representative bismuth-based ferroelectric material is SBT (SrBi2Ta2O9).
Concerning the ferroelectric material used in the FRAM, Japanese Unexamined Patent Publication (Kokai) No. 13-102543 teaches the use of a single crystalline ferroelectric thin film, as a ferroelectric material, for forming a capacitor in the FRAM. This publication, however, does not teach the method of producing semiconductor devices by using a single crystalline ferroelectric thin film grown on a single crystalline substrate, as in the present invention.
Japanese Unexamined Patent Publication (Kokai) No. 11-103024 teaches a semiconductor device of the structure in which a ferroelectric thin film (oriented polycrystalline thin film), having a plurality of crystalline particles arranged as a layer, is formed on the lower electrode in which crystals constituting a surface that comes in contact with the thin film are arranged on a plane (111).
Further, Foster et al., Journal of Applied Physics, 81, 2324, 1997, reports a thin PZT film having a large residual polarization charge (2Pr) obtained by forming (001) SrRuO3 as a lower electrode on (001) SrTiO3 and then forming a thin PZT (001) film by the MOCVD method.
A system LSI using a ferroelectric material for forming the capacitor as mentioned above must have very highly reliable, since it is used in equipment that deals with money data and data on individuals, such as IC cards, smart cards, etc. To realize a service life of ten years, as expected for these system LSIs, it is desired that the polarizing charge of the ferroelectric capacitor is as large as possible. With the ferroelectric capacitors fabricated by the conventional sputtering method, however, the amount of polarizing charge was mostly from 20 to 25 μC/cm2, and it was difficult to obtain, maintaining a high yield, ferroelectric capacitors satisfying the amount of polarizing charge of 30 μC/cm2 that is necessary for practical products. It is even more difficult to obtain a ferroelectric capacitor having the amount of polarizing charge of not smaller than 35 μC/cm2 necessary for improving the reliability of the product.